Vascular grafts are commonly used as soft tissue prostheses to replace or repair damaged or diseased veins and arteries. Conventional textile implantable prostheses are manufactured using yarns made of biocompatible and biostable material. To maximize the effectiveness of prostheses, it is desirable that the prostheses have characteristics that closely resemble that of the natural body lumen. In particular, prostheses desirably exhibit long term wear and kink resistance. Typically, the yarns used in these types of textile constructions are subjected to strenuous conditions, such as constant rubbing against a stent during pulsation of blood. Such abrasive forces can result in weakening of conventional textile prosthesis made with polyethylene terephthalate (PET) yarns, which can result in loss of structural integrity, and in extreme cases graft failure. Thus, there is a need for more durable and lubricious yarns that are capable of being incorporated into vascular prostheses.
PTFE is used in numerous demanding applications due to its excellent physical properties, which include excellent high and low temperature performance, chemical resistance and lubricious properties. PTFE is particularly useful in medical devices such as vascular prostheses. Use of PTFE yarns for textile vascular prostheses has been limited because finished PTFE yarns suitable for use in medical devices are often not commercially available to medical device manufacturers. Unfinished PTFE yarns that are available, however, typically do not possess the physical characteristics necessary for such medical device uses, such as sufficient orientation, i.e. molecular alignment of the fibers, and the requisite uniform linear density. This creates problems when processing such yarns into a textile prosthesis. For instance, unfinished yarns may accumulate in the machine during the textile prosthesis manufacturing process or stretch to create a non-uniform prosthesis. Additionally, problems may occur when such prostheses having unfinished PTFE yarns therein are placed in a body lumen because such yarns may unexpectedly and undesirably stretch. Thus, the prostheses will not perform in a consistent and predictable manner. As such, these yarns are not suitable for use in medical devices without further processing.
Conventional means to finish PTFE yarns typically involve a heat drawing process. Heat drawing results in yarns with good orientation and uniform linear density which when incorporated into a textile vascular prosthesis exhibit predictable and consistent behavior, both in the textile manufacturing process and in vivo. However, it may be difficult to control and maintain the elevated temperature that is necessary for heat drawing and it may be expensive to obtain heat drawing equipment. Thus, conventional methods for drawing yarns suitable for use in implantable textile prostheses are less than satisfactory.
Accordingly, it is desirable to provide textile prostheses with improved lubricious properties comprising cold drawn PTFE yarns having have a uniform linear density and a highly oriented molecular structure and drawn using a convenient and inexpensive cold drawing process.